1. Field of the Invention
This invention relates to comminutaing materials, and more particularly to centrifugal mills.
The invention can find application in the mining, construction and chemical industries for dispersing and mechanochemical activation of solids, and also in research facilities for modelling automated production lines and for facilitating solutions associated with problems before science and technology.
2. Description of the Related Art
There is known a centrifugal ball mill of continuous action (SU, A, 395111) comprising a stationary housing having a cylindrical inner surface, a vibration feeding means, and separators rotatable on a shaft and having balls freely inserted into grooves and accurately locked in planes substantially perpendicular to the axis of rotation by the separators, the diameter of the balls reducing and the number of such balls increasing in the direction of feeding the material to be comminuted.
Comminution of materials in a continuous action centrifugal ball mill is based on crushing the material particles at the points of contact of the balls to which centrifugal forces caused by rotation of the separators are exerted with the cylindrical inner wall of the housing.
A characteristic feature of the centrifugal mill of this type is low power of impact pulses produced by the milling balls oscillating exclusively due to the lack of stability of their travel on the layer of material moving along the inner surface of the housing; in addition, the material tends to stick to the cylindrical wall of the housing to form a soft base, which reduces communition efficiency, hampers the flow of the material, and affects the function of the balls.
There is also known a continuous action centrifugal mill (cf., SU, A, 925386) comprising a feeder secured on a housing having a ribbed working surface and accommodating a separator arranged coaxially on a shaft and including a cavity filled with balls. A side wall of the separator has through holes corresponding to the diameter of the milling balls which enter the through holes during rotation of the separator to engage with the ribs of the housing.
This centrifugal mill operates as follows. Centrifugal forces generated due to rotation of the separator displace the balls to the inner wall of the separator and the balls are piled in a row of layers. Therewith, part of the balls in the layer adjacent to the wall enter the through holes of the separator. These balls are caused to roll and slide on the working surface of the housing periodically hitting the ribs, whereby the impact energy is transferred to the rest of the balls present in the cavity of the rotating separator, which due to different geometrical and dynamic conditions of interaction move randomly. Importantly, the greater the number of balls charged to the cavity of the separator, the higher is the frequently of ball interaction and the smaller is the distance they fly between impacts. Conversely, a reduction in the charge of balls in the cavity of the separator results in less frequent interaction between the balls, a greater distance they travel between the impacts, and longer time periods between impacts.
The initial material delivered from the feeder to the cavity of the separator is acted upon by the turbulent flows of air and randomly moving balls, and is forced via the through holes of the separator, which are open at points in time following the impacts of the balls, against the ribs on the working surface of the housing. The material is preliminarily treated in the cavity of the separator due to the dynamic interaction of the randomly moving balls, whereas the main and subsequent treatment stages of the material are based on collision of the balls against the ribs of the working surface of the housing. Therefore, the designation of balls randomly moving in the cavity of the separator is limited exclusively to ensuring a more prompt return of the balls present in the through holes of the separator to the working surface of the housing subsequent to their recoil from the ribs. At the same time, while performing this function, the balls present in the cavity of the separator obtain rotation pulses as they interact with the balls in the through holes to result in friction therebetween as well as in a loss of energy and wear of the balls. In addition, the balls present in the through holes of the separator are in contact with the walls of the through holes about an arc, which also promotes losses of energy for friction. Reducing the number of balls in the cavity of the separator causes less energy lost for friction, although extends the time of flight of the balls present in the through holes to consequently result in a reduction in the frequency of impacts delivered on the working surface of the housing. The random movement of the balls present in the cavity and in the through holes of the separator accelerates wear of the balls, slows down the comminution process and activation accompanied by losses of energy and failure to provide stable periodical vibration impact movement of balls at a high frequency of their interaction with the material being comminuted.
In addition, the heretofore described construction of the centrifugal mill in the horizontal or inclined positions fails to provide the sufficient level of activation and comminution fineness due to non-uniform distribution of the material at the top and bottom parts of the working surface of the housing.
In the case of vertical arrangement of the axis of the mill, accelerated velocity of the material under the forces of gravity reduces the dwelling time of the material at the working surface to result in less efficient material comminution process. When comminutins viscous materials, the output capacity of the mill tends to reduce, because the material adheres to the working surfaces to result in slowing down its movement toward the discharge hole. Also, this mill construction fails to provide uniform delivery of reagents directly to the working zone in the desired percentage.